Lactococcus lactis is one of the best studied bacteria. After its isolation more than 100 years ago, it first received attention as dairy bacterium because of its importance in cheese and butter fermentations. Following the development of genetic engineering, it quickly became the paradigm lactic acid bacterium. Today the genomes of three different strains of the genus L. lactis are elucidated and prototype genome-based complete metabolic models are developed. The development of the NI isin C ontrolled gene E xpression (NICE) system about 10 years ago greatly facilitated progress in many areas of research not only in Lactococcus itself, but also in all other lactic acid bacteria.

The NICE system is a straightforward, easy to use system (plug-and-play genetic toolbox) for strictly controlled expression of homologous and heterologous genes. The advantages of L. lactis as gene expression system over e.g. E. coli are that it is food grade (including the selection marker), does not produce endotoxins or inclusion bodies, it has very low protease activity, does not sporulate and it has only one membrane. At present, the NICE system is quickly growing into an important tool for expressing and studying prokaryotic and eukaryotic membrane proteins. Furthermore, the NICE system is growing beyond its initial role as a research tool and is used for the production of oral and live vaccines and for the large scale production (3000 L) of pharmaceutical proteins such as lysostaphin.